Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 291327
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
327 AM HST FRI MAY 29 2015

.SYNOPSIS...
A SURFACE RIDGE BUILDING FAR NORTHWEST OF THE STATE WILL BRING
GENTLE TO MODERATE TRADE WINDS ACROSS THE WESTERN ISLANDS TODAY...
BUT WINDS WILL REMAIN LIGHT ENOUGH TO ALLOW LOCALIZED LAND AND
SEA BREEZES. A PERSISTENT TROUGH LINGERING NEAR THE BIG ISLAND
WILL MAINTAIN LIGHTER WINDS WITH WIDESPREAD SEA BREEZES OVER THE
EASTERN HALF OF THE STATE. TRADE WINDS SHOULD INCREASE SOMEWHAT
ACROSS MOST OF THE STATE DURING THE WEEKEND...BUT CONTINUED ABOVE
NORMAL MOISTURE WILL KEEP SHOWERS ACTIVE ESPECIALLY ACROSS
WINDWARD AND MAUKA AREAS. TRADES ARE FORECAST TO DECREASE ONCE
AGAIN EARLY NEXT WEEK...WITH SCATTERED SHOWERS CONTINUING ACROSS
BOTH WINDWARD AS WELL AS SOME LEEWARD AND INTERIOR AREAS.

&&

.DISCUSSION...
SHOWERS HAVE DIMINISHED ACROSS MAUI COUNTY DURING THE LAST FEW
HOURS...AND ARE CURRENTLY DOTTING PARTS OF THE COASTAL WATERS WITH
MOSTLY DRY CONDITIONS ACROSS THE ISLANDS. ON THE SYNOPTIC SCALE...
A DEEP LAYERED LOW PRESSURE AREA REMAINS IN PLACE OVER THE NORTH
PACIFIC CENTERED ABOUT 1300 MILES NNE OF PHNL. A RIDGE AT THE SFC
AND ALOFT IS CENTERED FAR TO OUR WNW NEAR THE INTERNATIONAL
DATELINE. CLOSER TO THE ISLANDS...A WEAK SFC TROUGH EXTENDS NE
FROM THE BIG ISLAND. WEAK FLOW DUE TO THIS TROUGH PREDOMINATES
ACROSS THE EASTERN HALF OF THE STATE...WHILE GENTLE TO LOCALLY
MODERATE NE FLOW AROUND THE DISTANT SFC HIGH PREVAILS OVER THE
WESTERN ISLANDS. MIMIC-TPW SATELLITE IMAGERY DEPICTS A LARGE AREA
OF HIGH ATMOSPHERIC MOISTURE CONTENT EXTENDING FAR TO THE ENE OF
THE BIG ISLAND...WITH A TAIL OF ABOVE NORMAL MOISTURE TRAILING TO
THE WSW ACROSS MUCH OF THE STATE. THE 12Z SOUNDINGS SHOWED VERY
LITTLE CHANGE DURING THE PREVIOUS 12 HOURS...WITH INVERSIONS BASED
AROUND 8K FEET...AND SLIGHTLY ABOVE NORMAL PWATS NEAR 1.35 INCHES.

STRONG W/NW WINDS CONTINUE ON THE BIG ISLAND SUMMITS DUE TO THE
MID LEVEL TROUGH TO OUR NORTH...WITH THE CFHT SENSOR SHOWING
SUSTAINED WINDS CONSISTENTLY AROUND 50 MPH WITH GUSTS NEAR 60
MPH AT TIMES DURING THE NIGHT. A WIND ADVISORY REMAINS POSTED FOR
THE SUMMITS THROUGH 6 PM TODAY.

TODAY SHOULD BE SIMILAR TO THURSDAY...WITH NE BACKGROUND FLOW AND
LOCALIZED SEA BREEZES OVER THE WESTERN ISLANDS...AND LIGHT FLOW
WITH MORE WIDESPREAD SEA BREEZES OVER THE EASTERN ISLANDS. AREAS
OF ABOVE NORMAL MOISTURE LINGERING AROUND THE STATE MAY PRODUCE
MORE CLOUDINESS AND A BIT MORE SHOWER ACTIVITY THAN WOULD
OTHERWISE BE THE CASE ACROSS INTERIOR AND LEEWARD AREAS ONCE AGAIN
THIS AFTERNOON...BUT MOST OF THE SHOWERS SHOULD REMAIN ON THE
LIGHTER SIDE.

MODERATE TRADES WILL RETURN TO MOST OF THE STATE THIS WEEKEND...
AS HIGH PRESSURE BUILDS TO OUR NORTH. GUIDANCE HAS TRENDED
STRONGER WITH THE TRADE WIND FLOW ACROSS THE SMALLER ISLANDS ON
SATURDAY...PARTICULARLY KAUAI/OAHU...WITH LIGHTER WINDS AROUND
THE BIG ISLAND AS THE WEAK SFC TROUGH CONTINUES TO LINGER JUST TO
THE EAST. CONTINUED ABOVE NORMAL MOISTURE AND RELATIVELY WEAK
INVERSIONS SHOULD ALLOW FOR ACTIVE TRADE SHOWERS ACROSS WINDWARD
AND MAUKA AREAS. IT NOW APPEARS THAT THE EXTENT OF SEA BREEZES ON
THE SMALLER ISLANDS WILL BE QUITE LIMITED DUE TO THE EXPECTED
STRONGER TRADES...BUT WITH THE EXTRA MOISTURE IN PLACE WE COULD
STILL SEE ISOLATED TO WIDELY SCATTERED AFTERNOON SHOWERS DEVELOP
ACROSS SOME INTERIOR/LEEWARD AREAS...ESPECIALLY ON MAUI. THE KONA
COAST OF THE BIG ISLAND SHOULD SEE SOMEWHAT BETTER RAIN CHANCES...
AS IS OFTEN THE CASE DURING THE SUMMER MONTHS.

TRADES MAY WEAKEN SLIGHTLY EARLY NEXT WEEK AS THE SFC HIGH SHIFTS
NE OF THE STATE...BUT RECENT MODEL CONSENSUS MAINTAINS ENOUGH OF A
RIDGE TO OUR NORTH TO KEEP A GENERAL LIGHT TO MODERATE TRADE WIND
PATTERN IN PLACE OVER THE ISLANDS. THE NEXT MID/UPPER TROUGH WILL
PASS NORTH OF THE STATE MONDAY AND TUESDAY...POSSIBLY PROVIDING
SOME MODEST MID LEVEL INSTABILITY. THIS COMBINED WITH CONTINUED
ABOVE NORMAL MOISTURE COULD RESULT IN ENHANCED SHOWERS...BOTH IN
THE TYPICAL WINDWARD/MAUKA AREAS...AS WELL AS OVER INTERIOR/LEEWARD
AREAS ALONG LOCAL SEA BREEZES DURING THE AFTERNOONS.

LITTLE CHANGE IS INDICATED THROUGH THE MIDDLE AND LATER PARTS OF
NEXT WEEK...WITH GENTLE TO MODERATE TRADES AND ABOVE NORMAL
MOISTURE PERSISTING OVER THE STATE.

&&

.AVIATION...
A WEAK LOW PRESSURE THROUGH NE OF THE BIG ISLAND WILL MAINTAIN A
WEAK PRESSURE PATTERN ACROSS THE EASTERN PART OF THE STATE...
DOMINATED BY DAYTIME SEA BREEZES AND OVERNIGHT LAND BREEZES...WITH
GENTLE TRADES AND LOCAL SEA BREEZES ACROSS WESTERN SECTIONS.
ISOLATED TO SCATTERED SHRA WILL LIKELY DEVELOP ONCE AGAIN OVER THE
INTERIOR/LEEWARD SECTIONS THIS AFTERNOON...WITH SOME TEMPORARY
MVFR CIGS/VSBYS POSSIBLY AFFECTING SEVERAL OF THE TERMINALS.

NO AIRMETS ARE IN EFFECT AT THIS TIME. AIRMET SIERRA MAY BE
NEEDED FOR SOME AREAS THIS AFTERNOON AS CLOUDS AND SHOWERS DEVELOP
ALONG THE SEA BREEZES.

&&

.MARINE...
THERE WILL BE A SERIES OF SMALL SOUTHERLY SWELLS THROUGH SATURDAY.
A LARGER SOUTH SWELL IS EXPECTED DURING THE SUNDAY THROUGH TUESDAY
TIME PERIOD WITH SURF HEIGHTS EXPECTED TO REACH ADVISORY LEVELS.
THE LATEST DATA FROM THE AUNUU BUOY NEAR AMERICAN SAMOA SHOWS
SWELL HEIGHTS AND PERIODS STILL RUNNING NEAR WAVE WATCH GUIDANCE.
THIS SWELL WILL BEGIN TO REACH THE HAWAIIAN ISLANDS SUNDAY...WITH
PEAK OPEN OCEAN SWELL HEIGHTS OF 4 TO 5 FEET FORECAST TO OCCUR
SUNDAY NIGHT AND MONDAY. SWELL AND SURF WILL SLOWLY SUBSIDE MONDAY
NIGHT AND TUESDAY.

OTHERWISE...EXPECT ONLY A SERIES OF SMALL NORTHWEST SWELLS OVER
THE NEXT SEVERAL DAYS.

THE THURSDAY EVENING ASCAT PASS FOUND SOME 15 KT WINDS IN THE
ALENUIHAHA CHANNEL...WITH MOSTLY NE OR VARIABLE WINDS OF 10 KT
OR LESS ELSEWHERE ACROSS THE EASTERN COASTAL WATERS. WINDS AND
SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH THE WEEKEND. HOWEVER THE LARGE AND LONG PERIOD SOUTH SWELL
MENTIONED ABOVE WILL LIKELY CAUSE LOCALLY HAZARDOUS CONDITIONS
NEAR SOUTH FACING HARBOR ENTRANCES FROM SUNDAY THROUGH MONDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM HST THIS EVENING FOR BIG ISLAND SUMMITS.

&&

$$

JACOBSON







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